Variable displacement hydraulic gear pump

ABSTRACT

A variable displacement hydraulic gear pump has a housing having fluid inlet and fluid outlet ports; and first and second gears rotatable in the housing. The first gear and the second gear are positioned in gear tooth engagement for at least a portion of the axial length of each. At least one of the first gear and the second gear is axially moveable, to vary the axial length of gear tooth engagement.

TECHNICAL FIELD

[0001] The present invention relates to hydraulic systems and hydraulic pumps, and more particularly, to hydraulic gear pumps which may be operated over a variable displacement range.

BACKGROUND ART

[0002] Hydraulic systems employ various types of hydraulic pumps in different situations. When the hydraulic system requires a pump capable of variable displacement, it is known to use a reciprocating pump, a gear pump or a vane pump, the speed of which can be varied to achieve the desired flow.

[0003] Gear pumps may be of several types, including pumps having externally meshing gears, that is two gears having external teeth disposed in meshed relationship in a gear pump housing. A second type of gear pump has an internal/external meshing relationship. A ring-shaped outer gear having teeth on the inner diameter, and an externally toothed gear are disposed in meshed relationship in a housing.

[0004] Gear pumps have several advantages over other types of rotary pumps, and over reciprocating pumps, including the simplicity in construction and reliability in operation of gear pumps. Another advantage of certain gear pump designs is that the pump can be constructed to pump fluid in a reverse direction when the gear rotation is reversed. Alternatively, with the use of valves, a gear pump can be made to pump in the same direction, regardless of the direction in which the gears are rotated. Flexibility in pump usage for different pumping directions can be useful in some hydraulic systems. Such flexibility is more easily achieved with gear pumps than with other types of rotary pumps or with reciprocating pumps.

[0005] In spite of distinct advantages in using gear pumps, it has not been known to use gear pumps when the hydraulic system requires a pump of variable displacement at a fixed speed. Varying the pump rotational speed changes the pumping flow rate, but may substantially impact pump efficiency. It is known to continually operate a gear pump at maximum displacement, and to divert a portion of the flow from the gear pump when a reduced flow is required. U.S. Pat. No. 4,022,251 entitled “Variable Capacity Type Gear Pump”, teaches the use of ports in the pump casing surrounding the gears, with a control valve controlling the flow of by-passed fluid through the ports. A variable displacement gear pump of the internal/external gear mesh variety is shown in U.S. Pat. No. 4,097,204, entitled “Variable Displacement Gear Pump”. The internal gear is rotated about a fixed axis, and the external gear is driven by the internal gear about a controlled, moveable axis. Varying the eccentricity between the internal and external gears changes the depth of gear tooth mesh, and thereby the volume of fluid displaced. The aforementioned variable displacement gear pump designs are achieved with added complexity to the basic gear pump construction.

[0006] The present invention is directed to overcoming one or more of the problems as set forth above.

DISCLOSURE OF THE INVENTION

[0007] In one aspect of the invention, a variable displacement hydraulic gear pump comprises a housing having a fluid inlet and outlet ports. A first gear is rotatably disposed in the housing, and has first gear teeth and a first gear teeth axial length. A second gear is rotatably disposed in the housing, and has second gear teeth and a second gear teeth axial length. The first gear teeth and the second gear teeth are positioned in gear tooth engagement for at least a portion of the first gear teeth axial length and a portion of the second gear teeth axial length. At least one of the first gear and the second gear is moveable.

[0008] In another aspect of the invention, a method for operating a gear pump comprises providing a first gear and a second gear disposed in meshed relationship over a gear engagement axial length; and adjusting the gear engagement length.

[0009] In still another aspect of the invention, a hydraulic system comprises a hydraulic device having a variable input flow requirement; a source of hydraulic fluid; and a variable displacement hydraulic gear pump. The hydraulic gear pump includes a first gear rotatably disposed in the housing, and having first gear teeth and a first gear teeth axial length. A second gear is rotatably disposed in the housing, and has second gear teeth and a second gear teeth axial length. The first gear teeth and the second gear teeth are positioned in gear tooth engagement for at least a portion of the first gear teeth axial length and a portion of the second gear teeth axial length. At least one of the first gear and the second gear is moveable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is an axial cross-section of a variable displacement hydraulic gear pump according to the present invention;

[0011]FIG. 2 is a cross-sectional view of the variable displacement hydraulic gear pump shown in FIG. 1, taken along line 2-2 of FIG. 1;

[0012]FIG. 3 is a cross-sectional view of the variable displacement hydraulic gear pump shown in FIG. 1, taken along line 3-3 of FIG. 1;

[0013]FIG. 4 is a cross-sectional view of the variable displacement hydraulic gear pump shown in FIG. 1, taken along line 4-4 of FIG. 1;

[0014]FIG. 5 is a cross-sectional view of the variable displacement hydraulic gear pump shown in FIG. 1, taken along line 5-5 of FIG. 1;

[0015]FIG. 6 is an axial cross-section of a further embodiment of a variable displacement hydraulic gear pump according to the present invention; and

[0016]FIG. 7 is a schematic illustration showing a variable displacement hydraulic gear pump of the present invention in a hydraulic system.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Referring now to the drawings, and more particularly to FIG. 1, there is shown a first embodiment of a variable displacement hydraulic gear pump 10 of the present invention. Gear pump 10 includes a housing 12 having a base 14 and a cover 16.

[0018] Housing 12 defines ports 18 and 20 (FIG. 3), one of which serves as an inlet, and the other serves as an outlet, depending upon the manner in which gear pump 10 is operated, as will be described more fully hereinafter.

[0019] Housing 12 defines a space 22 and a chamber 24 separated from space 22 by a partition 26. Space 22 and chamber 24 are formed nearly completely within cover 16. Base 14 is secured to cover 16, to define closed spaces for space 22 and chamber 24. Base 14 includes a cavity 28 having an opening 30 thereto from outside gear pump 10.

[0020] A shaft 32 extends from outside gear pump 10 through opening 30 and cavity 28. A sliding seal 34 is disposed on shaft 32, retained on shaft 32 in a circumferential groove 36 of shaft 32. Seal 34 rides in cavity 28, against sides 38 of cavity 28.

[0021] A first gear 40 is disposed on shaft 32 and is an inner gear of a cooperating gear set including an outer, second gear 42 disposed in space 22. Second gear 42 is a ring-like gear, having internal teeth 44 thereon, shown in FIGS. 2 through 4, and comprises the outer gear of the gear set. First gear 40 has external teeth 46 thereon, also shown in FIGS. 2 through 4, and forms the inner gear of the gear set. External teeth 46 drivingly cooperate with inner teeth 44 of second gear 42.

[0022] Second gear 42 is constrained against axial movement between a shoulder 48 of cover 16 and an inner surface 50 of base 14. Inner teeth 44 extend substantially the entire axial length of second gear 42 between shoulder 48 and surface 50, and thus define a second gear teeth axial length. Second gear 42 is rotatably retained in space 22, which extends partially around first gear 40. Second gear 42 rotates through space 22.

[0023] External teeth 46 of first gear 40 extend substantially the entire axial length of first gear 40 and define a first gear teeth axial length of first gear 40. Axes of rotation for first gear 40 and second gear 42 are radially offset, such that, along an arc of each first gear 40 and second gear 42, the inner teeth 44 and external teeth 46 thereof mesh, defining a region of gear tooth engagement. The axial length of the gear tooth engagement may vary, depending upon the position of first gear 40 in chamber 24. Shaft 32 is slidable axially through opening 30, and first gear 40, secured to shaft 32, is axially movable in chamber 24, which includes an elongated area into which first gear 40 may extend beyond second gear 42. The axial length of the gear tooth engagement between first gear 40 and second gear 42 is that portion of the first gear teeth axial length and the second gear teeth axial length which “overlap”, and are, therefore, physically engaged in chamber 24.

[0024] As shown in FIGS. 3 and 4, a sealing body 52 is disposed in chamber 24. Body 52 is secured to or is integral with cover 16 and has an inner surface 54 having a radius of curvature to provide a sealing relationship with first gear 40, and an outer surface 56 having a radius of curvature to provide a sealing relationship with inner teeth 44 of second gear 42, as is known in gear pump art. Body 52 thereby separates a first region 58 from a second region 60. Port 18 is associated with first region 58, and port 20 is associated with second region 60. One of first region 58 and second region 60 operates as an inlet zone and the other as an outlet zone, depending upon the manner in which pump 10 is operated, as will be described in greater detail hereinafter.

[0025] Shaft 32 is connected to drive means, not shown, and axially translating means also not shown, which can rotate shaft 32 and adjust the axial position of shaft 32, respectively.

[0026] A second embodiment of a variable displacement hydraulic pump 70, according to the present invention, is shown in FIG. 6. Pump 70 includes a first gear 40 on shaft 32 axially translatable in chamber 24, substantially as described for pump 10, and as shown in FIGS. 1-5. However, instead of a ring-like second gear 42, pump 70 further includes a second gear 72 which is an externally toothed spur gear or the like, positioned for engagement with first gear 40. Second gear 72 thereby includes external teeth which engage external teeth 46 of first gear 40. Second gear 42 is rotatably retained in a modified housing 74, including a cover 76 surrounding the gear couple defined by first gear 40 and second gear 72. First gear 40 and second gear 72 rotate in housing 74, passing closely to cover 76 at outer edges of the gears 40 and 72. Neither a partition 26 nor sealing body 52 is required. Inlet and outlet chambers, not shown, are defined on opposite sides of the gear couple formed by first gear 40 and second gear 72. Ports, not shown, are provided in housing 74, in communication with the inlet and outlet chambers on opposite sides of a gear tooth engagement region 78 of gears 40 and 72.

[0027]FIG. 7 illustrates a hydraulic system 90 in which a gear pump 100 embodying the present invention is used. Gear Pump 100 maybe similar to first embodiment gear pump 10 or second embodiment gear pump 70. Gear pump 100 receives hydraulic fluid from a hydraulic fluid source 102 via a conduit 104. Pump 100 supplies hydraulic fluid via a conduit 106 to a work machine 110, which includes a frame 112 and a hydraulic device 114. In FIG. 7, hydraulic device 114 is shown as a hydraulic cylinder operating between frame 112 and an arm 116 or the like of work machine 110. However, it should be understood that hydraulic device 114 may be any of many different hydraulic devices having a variable input flow requirement, including hydraulic motors and other types of hydraulic actuators. Hydraulic device 114 may operate between or with any of many components in a machine, and need be secured to a frame member as shown in FIG. 7. The hydraulic cylinder shown as hydraulic device 114 operating between frame 112 and arm 116 is merely an illustrative example of a system in which the present invention can be used advantageously. It should not be considered as a limitation on possible uses or applications of the present invention, nor as a limitation on the claims to follow.

Industrial Applicability

[0028] In use, pump 10 or pump 70 can be provided in a hydraulic system 90 including a hydraulic device 114 requiring a variable flow of hydraulic fluid thereto. Either pump 10 or pump 70 can be adjusted to thereby increase or decrease the displacement per revolution of the pump.

[0029] For gear pump 10, shown in FIGS. 1-6, from a position shown in FIG. 1, if an increased fluid displacement is required, an axial translation actuator, not shown, is activated to withdraw a portion of shaft 32 from housing 12. Thus, seal 34 is retracted further into cavity 28, and first gear 40 is caused to engage along an axially longer distance with second gear 42. Similarly with pump 70 shown in FIG. 6, as shaft 32 is withdrawn to a greater extent from housing 12, and seal 34 is retracted further into cavity 28, first gear 40 is caused to engage second gear 72 along an axially longer distance. Thus, the portion of gear tooth engagement between the first gear teeth axial length and the second gear teeth axial length is increased. The longer axial engagement length between first gear 40 and either second gear 42 or second gear 72 increases the pumping flow per revolution of pumps 10 or 70, respectively.

[0030] Conversely, if a lesser displacement is required from pump 10 or pump 70, shaft 32 is moved further into housing 12, thus moving an additional axial length of first gear 40 away from second gear 42 or second gear 72, respectively. The corresponding decrease in the axial length of gear tooth engagement between the first gear teeth axial length and the second gear teeth axial length decreases the pumping performance of pump 10 or pump 70.

[0031] Adjusting the gear engagement axial length for either gear pump 10 or gear pump 70 adjusts the displacement performance of gear pump 10 or gear pump 70, even if the rotational speed of the gears remains constant. As is known in the art, first gear 40 is driven, and either second gear 42 or second gear 72 of pumps 10 and 70, respectively, is driven through engagement with first gear 40. It is possible, in some applications of gear pumps, that the second gear will also be driven. The inlet region of chamber 24 is that region 58 or 60 in which the rotation of gears 40 and 42 or 72 results in the separation of gear teeth engagement. The region 58 or 60 of chamber 24 in which the gear teeth rotate into engagement functions as the outlet. Thus, in the embodiment shown in FIGS. 2 through 5, if first gear 40 is rotated clockwise, first region 58 functions as an inlet region, with port 18 being an inlet port; and second region 60 functions as an outlet region, with port 20 being an outlet port. If first gear 40 is rotated in a counterclockwise direction as shown in FIGS. 2 through 5, second region 60 functions as an inlet region, with port 20 being an inlet port; and first region 58 functions as an outlet region, with port 18 being an outlet port.

[0032] The present invention retains the advantages of gear pumps, including simplicity in structure, flexibility in application and reliability in use, while also incorporating variability in the pumping capacity a fixed speed without complicated external system valving or pump casing porting.

[0033] Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims. 

1. A variable displacement hydraulic gear pump comprising: a housing having fluid inlet and outlet ports; a first gear rotatably disposed in said housing, and having first gear teeth and a first gear teeth axial length; a second gear rotatably disposed in said housing, and having second gear teeth and a second gear teeth axial length; said first gear teeth and said second gear teeth positioned in gear tooth engagement for at least a portion of said first gear teeth axial length and a portion of said second gear teeth axial length; and at least one of said first gear and said second gear being axially moveable.
 2. The gear pump of claim 1, one of said first gear and said second gear being a ring gear having internal teeth thereon.
 3. The gear pump of claim 2, the other of said first gear and said second gear having external teeth thereon.
 4. The gear pump of claim 2, one of said first gear and said second gear being axially restrained in said housing.
 5. The gear pump of claim 2, including a shaft axially translatable in said housing, and one of said first gear and said second gear disposed on said shaft.
 6. The gear pump of claim 5, the other of said first gear and said second gear axially restrained in said housing.
 7. The gear pump of claim 1, each said first gear and said second gear having external teeth thereon.
 8. The gear pump of claim 7, one of said first gear and said second gear being axially restrained in said housing.
 9. The gear pump of claim 1, one of said first gear and said second gear being axially restrained in said housing.
 10. The gear pump of claim 1, including a shaft axially translatable in said housing, and one of said first gear and said second gear disposed on said shaft.
 11. A method for operating a gear pump comprising the steps of: providing a first gear and a second gear disposed in meshed relationship over a gear engagement axial length; and adjusting said gear engagement axial length.
 12. The method of claim 11, including restraining one of said first gear and said second gear while axially positioning the other of said first gear and said second gear.
 13. The method of claim 11, including providing an internally toothed gear and an externally toothed gear, and sliding said externally toothed gear axially in said internally toothed gear.
 14. The method of claim 13, including restraining said internally toothed gear against axial movement while moving said externally toothed gear axially.
 15. The method of claim 11, including providing first and second externally toothed gears and moving at least one of said gears axially.
 16. The method of claim 15, including restraining one of said gears against axial movement.
 17. A hydraulic system comprising; a hydraulic device having a variable input flow requirement; a hydraulic fluid source; and a variable displacement hydraulic gear pump in fluid flow relationship between said fluid source and said hydraulic device, said gear pump including; a housing; a first gear rotatably disposed in said housing, and having first gear teeth and a first gear teeth axial length; a second gear rotatably disposed in said housing, and having second gear teeth and a second gear teeth axial length; said first gear teeth and said second gear teeth positioned in gear tooth engagement for at least a portion of said first gear teeth axial length and a portion of said second gear teeth axial length; and at least one of said first gear and said second gear being axially moveable.
 18. The hydraulic system of claim 17, one of said first gear and said second gear being a ring gear.
 19. The hydraulic system of claim 17, each said first gear and said second gear being externally toothed gears.
 20. The hydraulic system of claim 17, one of said first gear and said second gear being restrained against axial movement. 